This invention relates to a method for repairing or otherwise treating metal components by brazing. In particular it relates to a method for preventing flow of brazing alloy onto selected surfaces and into internal cavities of components being brazing, and to a stopoff material for use as a barrier to flow of braze alloy.
Holes, cracks, chips, and other defects in metal components are often repaired by furnace brazing. When such components have internal cavities, as is the case with, for example, gas turbine engine airfoils, the repair alloy has a tendency in some instances to flow into the internal cavities. This is not desirable because when the alloy solidifies in the internal cavities, it changes the internal configuration, weight, and weight distribution of the component to other than the engineered parameters, and may even clog internal cavities. As such, slurries, preforms, and putties have been used as internal maskant, often referred to as internal stopoff, to prevent the flow of braze alloy into internal cavities during repair.
It is also desirable to prevent the flow of braze alloy into slots and onto certain surfaces during brazing, such that there is a need for a way to form barriers to flow of braze alloy.
Briefly, therefore, the invention is directed to a method for forming a barrier to flow of brazing alloy on a component to be treated by brazing. A quantity of stopoff slurry comprising an oxide powder and a binder is applied to a surface of the component. The stopoff slurry is dried to set the binder and form a hardened stopoff material on the surface to form a barrier to flow of brazing material.
The invention is also directed to a method for preventing flow of brazing alloy into an internal cavity of a component being repaired by brazing. The internal cavity is charged with a stopoff slurry comprising powdered oxide and a binder. The stopoff slurry is dried to set the binder and form a hardened stopoff material in the internal cavity which seals openings into the internal cavity.
The invention is further directed to stopoff slurry for application to internal cavities of components to be repaired by brazing to seal the internal cavities and prevent the flow of brazing alloy into the internal cavities, the stopoff slurry comprising alumina and a polyethylene oxide binder, the polyethylene oxide binder comprising polyethylene oxide and water.